<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .left-box,
    .right-box {
      width: 200px;
      height: 200px;
      background-color: pink;
      float: left;
    }

    .content-box {
      height: 300px;
      width: 100%;
      float: left;
      background-color: red;
    }
    .content {
      background-color: rgb(57, 17, 23);
      /* width: 100%; */
      height: 230px;
      margin: 0 200px;
    }

    .left-box {
      margin-left: -100%;
    }

    .right-box {
      margin-left: -200px;
    }

    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }
  </style>
</head>

<body>
  <div class="container">
    <div class="content-box">
      <div class="content"></div>
    </div>
    <div class="left-box"></div>
    <div class="right-box"></div>
  </div>
</body>

</html>